1The Field of the Invention
The present invention relates to a method and apparatus for determining, in the laboratory, the rate and type of hydrocarbon generation by a hydrocarbon source.
2. The Prior Art
The total amount of hydrocarbons that can be generated and the relative amounts of oil and gas in these hydrocarbons depend upon the composition of the parent kerogen in the petroleum source bed. Kerogen is the insoluble organic matter in sedimentary rock which is capable of generating hydrocarbons upon being heated.
Two broad types of dispersed kerogen can be recognized in sediment Type I, commonly referred to as sapropelic kerogen, contains amorphous algal remains, enriched in long chain aliphatic side branches and has an original high hydrogen content and relatively low oxygen/carbon ratio Upon thermal maturation, sapropelic kerogen yields mainly oil. Type III, referred to as humic kerogen, consists of land-plant derived lignitic and cellulosic constituents and is poor in aliphatic side chains. It has a low hydrogen content and a relatively high oxygen/carbon ratio. Upon thermal maturation, humic kerogen yields mainly gas. A mixture of humic and sapropelic kerogen, commonly referred to as Type II, will yield both oil and gas upon thermal maturation.
Heating kerogen causes thermal degrading in a predictable manner by releasing hydrocarbons and condensing the solid organic structure. The maturation of kerogen can be accelerated by conducting the reaction in an oxygen free atmosphere at temperatures higher than those commonly encountered in natural systems. Heating kerogen isothermally at elevated temperatures and pressures in the presence of water is a process referred to variously as hydrous pyrolysis, simulated maturation or sealed vessel pyrolysis.
The explorationist must correctly model the rate of oil and gas generation to prepare an estimate of the potential hydrocarbon volume in a frontier basin. Most previously published studies of the kinetics of oil and gas generation from hydrocarbon source material have been done using Rock-Eval pyrolysis. This is a popular method because the instruments are readily available. The procedure involves heating a sample, in a flowing helium stream, from room temperature to 550.degree. C. in 30 minutes. This is reIatively fast but the results are sensitive to sample texture and temperature measurement and control. Data analysis is complicated by the non-isothermal nature of the experiment.
Better quality kinetic data is obtainable from isothermal experiments in a closed system. Hydrous pyrolysis involves isothermal heating of the source material with water in a closed system, but product recovery problems have limited its application to qualitative studies of oil and bitumen generation.
The better examples of the prior art in this area are "A Laboratory Study Of Petroleum Generation By Hydrous-pyrolysis" by Winters et al. Advances in Organic Geochemistry, 1981 M. Bjoroy ed. New York Wiley 1983, pp. 524-532; "Comparison of Methods for Measuring Kerogen Pyrolysis Rates and Fitting Kinetic Parameters" by Burnham et al. UCRL-95660 193rd Meeting of the American Chemical Society, Denver, Colo. (Apr. 5, 1987); "Comparison between natural and artificial maturation series of humic coals from the Mahakam delta, Indonesia" Monthioux et al. Org. Geochem. Vol. 8, No. 4, pp. 275-292, 1985; and "The microscale simulation of maturation: outline of a new technique and its potential applications" Horsfield et al. Geologisohe Rundsohau 78/1 pp. 361-374 Struttgart 1989.
The Winters et al. publication is of particular interest in that it teaches the use of a closed reactor for heating kerogen, oil shale or hydrocarbon source materials, controlling and recording temperature at a specific value, means to purge the reactor with inert gas, hot transfer to a recovery vessel of the volatile products in a batch method, recovering bitumen from the reactor chamber through the use of solvents, and sampling the gases recovered and venting the rest. While this is somewhat similar to the present invention, it does not utilize a sample holder to confine the solids, use oxygen purged water, recover soluble bitumen from the sample holder by washing with solvents, or recover the low boiling oils from the water by a second cryogenic transfer with dryer means for removing the water. Thus the present invention enables a more complete analysis of the hydrocarbon sample.
The Monthioux et al. and Horsfield et al. articles describe methods for artificially maturing kerogen in closed systems in the absence of water. These methods have been used only for qualitative characterization of products resulting from kerogen maturation.